This application claims the benefit of Korean Patent Application No. 2000-10300, filed on Mar. 2, 2000, which is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of the Invention
The present invention relates to liquid crystal displays (LCD). More particularly it relates to an improvement in the LCD lines which drive the liquid crystal cells to display information.
2. Discussion of the Related Art
An LCD device comprises an LCD panel having upper and lower substrates that are spaced apart and opposed to each other and that have a liquid crystal layer there between. The upper substrate includes a color filter layer and a common electrode formed on the color filter layer. The lower substrate includes a switching element, such as a thin film transistor (TFT), and a pixel electrode.
The common electrode and the pixel electrode apply an electric field across the liquid crystal layer. The TFT serves to operate the pixel electrode using signals from an external drive circuit. The TFT includes a gate electrode, a source electrode, and a drain electrode. The gate electrode is connected to a gate line, the source electrode is connected to a data line, and the drain electrode is connected to the pixel electrode. The gate and source electrodes are connected to the external drive circuits through gate and data pads, respectively, formed at their terminals.
The external drive circuit comprises a gate drive circuit that drives the gate electrode and a data drive circuit that drives the source electrode. Techniques for connecting the drive circuit to the LCD panel include WB (wire bonding), COB (chip on board), TAB (tape automated bonding), and COG (chip on glass).
For a low resolution LCD it is easy to connect drive circuit leads on a PCB (printed circuit board) to the LCD panel since the number of leads is small. However, for a high resolution LCD, it is not so easy to connect drive circuits having a large number of leads to a PCB. For example, an LCD having a resolution of 600xc3x97800 (SVGA) has 600xc3x97800xc3x973 pixels, which are all connected to drive circuits and thus requires an involved connecting process.
The TAB technique has been introduced to address the problem described above. FIG. 1 shows a typical TAB technique. As shown in FIG. 1, a tape carrier 53 has a drive circuit 51 mounted thereon. The package in which the drive circuit is mounted on the tape carrier is referred to as a TCP (tape carrier package). In other words, a TCP 50 has the drive circuit 51. The LCD panel 20 and the PCB 52 are connected to the drive circuit 51 through the tape carrier 53. The TAB technique uses an inner lead bonding (ILB) process that connects the tape carrier to the chip using heat and pressure, and an encapsulation process that applies an epoxy-based resin on the chip. The TAB technique also includes an outer lead bonding (OLB) process that connects the outer leads to the pads on the PCB 52 and to the gate or data pads on the substrate, respectively.
Referring now to FIG. 2, gate drive circuits 100G are placed along the left side of the LCD panel, and data drive circuits 100D are placed across both the upper and lower sides of the LCD panel. Such a structure is referred to as a dual-bank structure. For an LCD having a resolution of 1600xc3x971200xc3x973 (UXGA), each of the typical data drive circuits 100D has 384 channels that can control 384 data lines. The number of the data and gate lines is thus 1600xc3x973 and 1200, respectively. Therefore, 14 drive circuits are required to control all of the 1600xc3x973 data lines. In the conventional dual-bank structure, seven drive circuits are arranged across both the upper and lower sides of the LCD panel, respectively. The seven data drive circuits mounted on the lower portion are connected to 2400 data lines. The data drive circuits D1 to D6 are each connected to 384 data lines, but the outmost data drive circuit D7 is connected to only 96 data lines. As shown in FIG. 2, the intervals between adjacent drive circuits are all xe2x80x9caxe2x80x9d and the seven data drive circuits are symmetrically arranged with respect to the center line xe2x80x9cCxe2x80x9d of the LCD panel 20. However, as explained in more detail below, when the intervals between the data drive circuits are all equal a resistance difference occurs in the wiring region (see FIG. 4).
FIG. 3 is an enlarged view illustrating a portion F1 of FIG. 2. Each data line has a display line d-n located on a display region (d-384 and d-385 are shown), a leadout line L-n located on a wiring region (L-384 and L-385 are shown), and a terminal line T-n located on a pad region (T-384 and T-385 are shown). Each terminal line T-n connects to a corresponding data drive circuit. As shown in FIG. 3, the last data line d-384 of a data drive circuit D1 and the first data line d-385 of a data drive circuit D2 have almost the same wiring distance. That is, the readout line L-384 and the leadout line L-385 have almost the same length. However, this is not the case in portion F2, shown in FIG. 4, which is an enlarged view of portion F2 of FIG. 2.
In FIG. 4, the last leadout line L-2304 connected to a data drive circuit D6 and the first leadout line L-2305 connected to a data drive circuit D7 differ significantly in length, resulting in a resistance difference between the leadout line L-2304 and L-2305. Such a resistance difference between adjacent leadout lines causes shadowing (uneven brightness) and distortions (such as deformations of liquid crystal drive waveforms and crosstalk).
FIG. 5 shows a simplified LCD panel having only 14 data lines, with each data drive circuit having only three channels. As shown, as a data drive circuit is positioned farther away from the first data drive circuit D1, the difference in length between the leadout lines of adjacent last and first data lines becomes greater. Namely, if all intervals between adjacent data drive circuits are equal, and if the data drive circuits are symmetrical about the center of the display, the lengths of the leadout lines of the last data lines become greater as a data drive circuit is positioned farther from the first data drive circuit D1. This causes a resistance difference between the readout lines of the adjacent last and first data lines. With regard to FIG. 5, the greatest difference in length between adjacent leadout lines occurs between the leadout line of the last data line connected to the data drive circuit D4, specifically data line d-12, and the leadout line of the first data line connected to data drive circuit D5, specifically d-13.
To alleviate display distortions due to resistance differences described above, one technique employs a method of adjusting the widths of the data lines to compensate for the RC (Resistancexc3x97Capacitance) delay. See U.S. Pat. No. 5,757,450. However, for a high resolution LCD device with a large number of data lines, it is rather difficult to accurately design and fabricate the data lines to compensate for the RC delay.
The problem described above results from the outermost data drive circuit having more channels than data lines. For example, the outermost data drive circuit D5 of FIG. 5 has three channels but connects to only two data lines. Such a problem could be addressed by employing data drive circuits in which all channels connect to a data line. For example, a liquid crystal display conceivably could use data drive circuits having 300 channels each to drive 4800 data lines. However, 16 data drive circuits would be required, leading to high production costs due to the additional data drive circuits and to their interconnections. Furthermore, data drive circuits with 300 channels would have to be designed and manufactured to replace those currently existing. Therefore, a display having reduced distortions caused by wiring resistance differences would be beneficial.
Accordingly, the present invention is directed to a display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An advantage of the present invention is that it can provide a display device having good display characteristics. Beneficially, that display device is a liquid crystal display device or an X-ray display device that includes data lines driven by display drivers.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, is a display device having a display region with a plurality of data lines, a pad region with a plurality of pads that electrically connect to terminal lines, a wiring region with a plurality of leadout lines that interconnect the terminal lines to the data lines, a plurality of first data drivers, each having N channels that electrically connect to N terminal lines. The display device further includes a second data driver having N channels that electrically connect to M terminal lines, where M is less than N. The first data drivers are spaced apart by equal intervals and each of the first data drivers are centered on N data lines. The second data driver is spaced from an adjacent first data driver by an interval that is less than the intervals between the first data drive circuits.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.